The source is a hot small black body (globar). Two metallic ellipsoidal mirrors collect and focus the radiation. The source is placed on the first focus of one mirror and its second focus is also the first focus of the other (collector). In the second focus of the collector there is the sample. A few mm above on the same optical line there are the filters and the pyroelectric detector. The total weight of the device is 5 kg.
The filters are annular holes on the aluminum film on silicon substrate: the filter are in both site of the silicon wafer. The SEM pictures of a region of filter having central frequency 10.5 THz filter is shown on side. The periodic square cell has a pitch 7 µm, each ring has an outer diameter 4.9 µm with a groove of 0,5 µm. The structure in this case is made by about half million of annular holes.